It is known that in forming a multi-color image comprising image elements in a first color which along at least part of their circumference adjoin image elements of one or more following colors to generate separate color images which are each built up from image dot patterns of colored toner powder. These separation images are transferred to an intermediate support to join them to form a multi-color image and the multi-color image thereafter being transferred from the intermediate support to an image receiving material.
Apparatus and methods utilizing such techniques are described, inter alia, in Japanese Patent Application Nos. 58/44459, 58/95362, and UK Patent 1 277 233. One problem which arises in performing these methods is the occurrence of register errors: the separation images are applied to the intermediate support with a shift relative to one another.
Causes of these register errors include tolerances in the parts of the apparatus in which the method is performed and wear of the moving parts of such apparatus. As a result of a register error, image elements of different separation images which are required to adjoin one another in the multi-color image, will locally overlap one another while in other places they are displaced from one another.
The overlap of image elements may result in a loss of information while incomplete adjoining of location of image elements results in the multi-color image showing the background (normally white) of the receiving material between the image elements.
If, for example, mixed colors are produced by means of opaque colored toner powders, by printing fine image dots indistinguishable to the eye in a first, second and any following color in the correct ratios next to one another, a register error also gives rise to problems.
Since image dots of the different separation images then completely or partially overlap one another, there is an incorrect ratio in the image dots of the separation colors and hence the mixed color is different from the required color. The above defects in the final multi-color image are all the more disturbing the larger the register error.
Accordingly, it is an object of the present invention to render substantially invisible the adverse effects of any register error in the multi-color image.